CT and MRI transformed structural brain imaging, but epilepsy surgery also needed ways to see brain function. PET and SPECT added metabolic and perfusion information that could reveal abnormalities even when structural imaging was normal.
Why structure was not enough
EEG could show electrical abnormalities and MRI could show anatomy, yet some people with drug-resistant focal epilepsy had no visible lesion or had findings that did not match the seizure network.
Functional imaging offered another type of evidence.
PET and cerebral metabolism
Positron emission tomography allowed regional brain metabolism to be measured using radiotracers such as FDG.
Interictal FDG-PET often shows reduced metabolism in regions associated with focal epilepsy, particularly temporal-lobe epilepsy, although the abnormal area may extend beyond the true seizure-onset zone.
SPECT and cerebral blood flow
Single-photon emission computed tomography can measure regional perfusion.
If tracer is injected rapidly during a seizure, ictal SPECT can show increased perfusion associated with seizure activity. Interictal SPECT provides a comparison state.
Subtraction techniques
Computerised subtraction of interictal from ictal SPECT, often coregistered with MRI, improved the ability to visualise perfusion change.
These techniques became particularly useful in MRI-negative or discordant presurgical cases.
Functional imaging becomes one piece of a larger puzzle
PET or SPECT rarely determines surgery by itself. Findings are interpreted alongside seizure semiology, scalp EEG, MRI, neuropsychology and sometimes invasive monitoring.
The historical development of epilepsy surgery increasingly became a story of converging evidence rather than one decisive test.
Newer tracers and quantitative methods
Research has explored receptor-binding tracers, amino-acid imaging, inflammation markers and more automated quantitative analysis.
FDG-PET remains the most established PET technique in routine presurgical epilepsy assessment.
Why the history still matters
PET and SPECT helped establish a key principle: epileptogenic brain dysfunction can be physiologically abnormal even when conventional structural imaging looks normal.
Related reading
Sources and further reading
Evidence checked: September 2026.